1. Field of the Invention
This invention relates to an apparatus and a method of supporting a load (such as an automobile) that is subject to rapid weight fluctuations (due to braking, cornering, accelerating, pulling a trailer, etc.). The support is precisely matched to the weight of the load at each instant, and substantially eliminates both vibration and disturbance otherwise caused by road irregularities.
2. Description of the Related Art
Suspension systems in use today are compromised in their design due to the wide variety of conditions that they must accommodate. The weight of passengers and cargo varies widely, as do loads imposed by yawing, pitching, and rolling forces. Compromises have resulted in instability while cornering and/or braking, changing vehicle height under varying loads, and unchanging vehicle height at widely varying speeds. For example, great handling, sleek, low slung sports cars can be difficult to enter or exit and high load capacity trucks with elevated beds can be difficult to load and unload. Either the sports car or the truck driver may find it difficult to access drive up windows or automated teller machines.
Numerous designs have been proposed to alleviate problems and shortcomings with conventional suspensions. Some have advocated the use of complex sensors and control units (e.g. U.S. Pat. No. 5,037,128 to Okuyama et al., issued Aug. 6, 1991. Others have required the combined use of hydraulics, pneumatics, and electronics to relieve some of the symptoms of compromise (e.g U.S. Pat. No. 4,934,731 to Hiwatashi et al., issued Jun. 19, 1990). Most of the efforts to address the ideal suspension have been addressed in a piecemeal fashion. Several patents address forces generated while turning, accelerating, or braking (U.S. Pat. No. 5,566,970 to Lin, issued Oct. 22, 1996, U.S. Pat. No. 5,401,053 to Sahm et al., issued Mar. 28, 1995, and U.S. Pat. No. 4,573,702 to Klem, issued Mar. 4, 1986). Other patents addressed ride height controls as well (U.S. Pat. No. 5,222,759 to Wanner, issued Jun. 29, 1993, U.S. Pat. No. 4,867,474 to Smith, issued Sep. 19, 1989, or U.S. Pat. No. 3,831,969 to Lindblom, issued Aug. 27, 1974).
Citroen installed hydro-pneumatic suspensions in production cars, typified by the prior art shown in FIG. 1A. The hydro-pneumatic suspension of FIG. 1 comprises a hydro-pneumatic spring 1A10 that supports a portion of a vehicle frame 1A17, which carries part of the vehicle load.
The pneumatic spring comprises a case consisting of a hollow cylindrical body, open at one end and having small, restricted openings 1A49 through a circular disk that otherwise closes the other end of the body. The cylinder is designed to contain fluid under pressure, and has an additional opening in the side of the cylinder near the closed end fluidly connected to a passage 1A35. The restricted openings and side opening provide fluid paths for the admission or release of pressurized fluid from the cylinder. The exterior radial surface of the case has an integral step 1A12 which provides a bearing surface for the frame member 1A17 to rest.
The frame member 1A17 provides support for a load, such as a vehicle (not shown), whose weight is transferred by the frame member to the integral step on the exterior radial surface of case 1A16.
A rod 1A19 is secured to and physically supports a piston 1A21. The rod is a structural member which maintains a specified spatial relationship between the piston 1A21 and a wheel support 1A40. The piston 1A21 slides within the interior bore of cylinder 1A16 yet maintains a pressure tight fit within the bore of the cylinder to provide a fluid seal between the cylinder 1A16 and piston 1A21.
A variable volume chamber 1A33 is defined by the space within case 1A16 between piston 1A21 and the closed end of case 1A16. The volume of the chamber 1A33 can be increased or decreased by forcing or releasing, respectively, pressurized fluid into the chamber through either the cylinder side opening or through the restricted openings. The variation in the volume of the chamber is reflected in the movement of piston 1A21 within the case 1A16.
Passage 1A35 fluidly connects a valve (not shown) to the variable volume chamber through the cylinder side opening. The valve controls the admission of fluid into variable volume chamber 1A33 or the release of fluid from the chamber. Movement of fluid through passage 1A35 varies the length or separation of wheel support 1A40 relative to the case 1A16 and, thus, relative to the frame 1A17 under static conditions.
The wheel support 1A40 is secured to the end of rod 1A19 opposite piston 1A21 and configured to be secured to a wheel assembly to support the frame and its load relative to the ground.
A compressible gas 1A47 is contained within a pressure accumulator 1A84. The compressible gas is isolated from the operating fluid in the lower half of the pressure accumulator and in variable volume chamber 1A33 by a membrane 1A51. The expansion and contraction of the compressible gas results from movement of fluid through the restricted openings in the closed end of case 1A16. The pressure accumulator 1A84 provides an air spring for the operation of the prior art suspension. When the wheel assembly encounters a bump, the wheel support, rod, and piston are all pushed up against the downward force of the load. This forces operating fluid up through the restricted openings, and compresses the compressible gas. Conversely, the compressible gas in the pressure accumulator forces fluid back into the variable volume chamber once the wheel assembly crests the bump, extending the piston back to its original position. The restricted openings 1A49 allow the operating fluid to pass between the pressure accumulator and the variable volume chamber at a predetermined rate.
A check valve 1A57 restricts fluid flows between the pressure accumulator and the case through the restricted openings.
A hydro-pneumatic spring similar to that shown in FIG. 1A has been used as an automotive suspension for a number of years. The vehicle is supported on the frame member 1A17, which is in turn supported by a case 1A16 containing pressurized hydraulic fluid. The pressurized fluid is contained in a variable volume chamber 1A33 that is defined by case 1A16 and piston 1A21. The piston can slide in the bore of case 1A16 while maintaining a pressure tight seal with the bore of the case. Pressurized fluid may be added or released from the variable volume chamber through passage 1A35, raising or lowering the vehicle with respect to wheel support 1A40. Fluid in the variable volume chamber is supported by piston 1A21, which in turn is supported by wheel support 1A40 through rod 1A19. Restricted openings 1A49 permit fluid flow between the variable volume chamber 1A33 and pressure accumulator 1A84 through check valve 1A57. Fluid that flows into or out of the pressure accumulator displaces bladder 1A51, causing compressible gas 1A47 to compress or expand.
The operation of the prior art fluid spring combined the features of an air spring (pressure accumulator 1A84), a hydraulic level control (piston 1A21 and rod 1A19 moving within case 1A16 as fluid is admitted or released through passage 1A35), and a shock absorber (restricted openings 1A49 and check valve 1A57 dampen the vertical motion of wheel support 1A40). The fluid in variable volume chamber 1A33 both supports the vehicle at varying extensions of rod 1A19 and acts as a transmission medium between piston 1A21 and bladder 1A51, causing compressible gas 1A47 to compress or expand as wheel support 1A40 absorbs bumps. In this manner the height of the frame member 1A17 is controlled, and road shock is isolated from it.